<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    p:first-child{
        /* 同级第一个并且为p的元素 */
        color: red;
    }
</style>
</head>
<body>
    <h3>0000000</h3>
    <p>1111111</p>

    <div>
        <h3>2222222</h3>
        <p>3333333</p>
    </div>

    <div>
        <p>4444444</p>
        <p>5555555</p>
    </div>
</body>
</html>